70's Johnson 20hp bad idle, cuts out at top speed

[crocket15]

I have a 20 hp johnson that idles at "start", but as i switch it to "shift" and "slow" it sputters to a stop. I've heard about a slow speed adjustment, but i am new to outboard motors and have not explored much into mine. It also cuts out at top speed, the priming bubble on my fuel tends to be a little soft, but the motor will start right back up. Is it possible that my line can get some air bubbles in it? Or could it be something like a fuel filter or pump? It doesn't seem like a serious problem, but my inability to shift the motor while it idles is a bit of an ordeal. Can someone tell me where such an adjustment might be, and why my motor cuts out at full speed? Thanks!

 

[tashasdaddy]

Re: 70's Johnson 20hp bad idle, cuts out at top speed

Welcome to iboats. please always state the model number of you motor. you have 3 proper items for an outboard to run properly, compression, spark, carboration(fuel/air mixture). start with the basics, do you have a good crisp spark that will jump 3/8 of an inch. also borrow or buy a compression tester (screw in type) remove the spark plugs, insert the guage, and pull the rope 4 times for each cylinder. record the numbers and post them. these will tell use if you have a viable motor and which direction to continue. it's basic trouble shooting. good luck.

 

[F_R]

Re: 70's Johnson 20hp bad idle, cuts out at top speed

If you are referring to the wording on the twist grip tiller, they are never correct, only a guide. You don't have to be afraid of the slow speed mixture adjustment. Give it a tweak either direction till it idles the best.